<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>课堂练习</title>
  <style>
    /* 请给一个 200*200 的盒子，设置上边框为红色，其余边框为蓝色
    */
    div {
      width: 300px;
      height: 200px;
      /* border-top: 1px solid red;
      border-right: 1px solid blue;
      border-left: 1px solid blue;
      border-bottom: 1px solid blue; */
      /* 包含了四条边 */
      border: 1px solid blue;
      /* 层叠行，覆盖了上边框，顺序不能颠倒 */
      border-top: 1px solid red;
    }
  </style>
</head>
<body>
  <div></div>
</body>
</html>